Hybrid fin field-effect transistor structures and related methods

ABSTRACT

Semiconductor-on-insulator structures facilitate the fabrication of devices, including MOSFETs that are at least partially depleted during operation and FinFETs including bilayer fins and/or crystalline oxide.

RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 12/125,308, filed on May 22, 2008, entitled “Hybrid FinField-Effect Transistor Structures and Related Methods;” which is acontinuation application of U.S. patent application Ser. No. 11/001,166,filed Dec. 1, 2004, entitled “Methods of Forming Hybrid Fin Field-EffectTransistor Structures;” the entire disclosures of these applications arehereby incorporated by reference in their entireties.

FIELD OF THE INVENTION

This invention relates generally to semiconductor structures andparticularly to hybrid strained semiconductor-on-insulator structures.

BACKGROUND

As geometric transistor scaling becomes more difficult and lesseffective in providing adequate performance enhancements, there is anincentive to improve the performance of transistors by enhancing innatecarrier mobility by, e.g., application of strain to the semiconductorchannel material. Although process simplicity is maintained by theapplication of one type of strain (or one type of channel material) forboth NMOS and PMOS devices, overall performance would be greatlyimproved if it were possible to enhance the performance of each type ofdevice separately. Traditionally, this enhancement has beenincomplete—one type of channel material is typically used for bothdevice types, with selective application of strain to the channelmaterial for each device.

Devices are advantageously formed on semiconductor-on-insulator (SOI)substrates. Such substrates offer the benefits of an insulatingsubstrate, such as reduced parasitic capacitances and improvedisolation.

SUMMARY

The efficacy of the traditional approach for enhancing the performanceof NMOS and PMOS devices may be improved by additionally customizing thetransistor channel materials and their respective strain levelsselectively for NMOS and PMOS devices. This is particularly true foradvanced transistor geometries such as partially depletedsemiconductor-on-insulator (PDSOI) devices, fully depletedsemiconductor-on-insulator (FDSOI) devices, or fin field-effecttransistors (FinFETs).

Although schemes exist to utilize multilayer channel materials and/ortypes of strain for transistors (see, e.g., U.S. Ser. Nos. 10/456,926,10/164,665, 10/177,571, and 10/216,085, and U.S. Pat. No. 6,730,551, allof which are incorporated herein by reference), these schemes may not beeffective for FDSOI and PDSOI devices when the total desired channelthickness for each type of device is very small. Since some such schemesrely on the presence of two channels in the starting substrate, thisbilayer scheme may not allow the device type that utilizes the topchannel for conduction to operate in fully depleted mode (due to thetotal thickness of the two channels being too great for the device tomeet the FD maximum thickness criterion).

In accordance with the invention, NMOS and PMOS devices have channellayers of different materials and/or types of strain, each withpotentially a very thin thickness. Aspects of the invention includevariations in the starting substrate/channel layer structure and/or theprocesses used during device fabrication to create the final structure.For these solutions, Si—Ge alloys are used as exemplary materials. Ingeneral, it has been demonstrated that layers of Si—Ge with low Gecontents and/or under tensile strain are preferred for NMOS devices, andlayers with higher Ge content and/or under compressive strain arepreferred for PMOS devices. Other combinations of materials, includinggroup IV semiconductors such as alloys of Si, Ge, or SiGe with C; III-Vsemiconductors; and II-VI semiconductors may also be suitable.

In an aspect, the invention features a structure including (i) asemiconductor substrate, a first semiconductor layer including a firstsemiconductor material disposed over at least a first portion of thesubstrate, and a second semiconductor layer including a secondsemiconductor material disposed over at least a second portion of thesubstrate; (ii) a first MOSFET disposed on the substrate and including afirst MOSFET channel disposed in a portion of the first semiconductorlayer over a first insulating material, the first MOSFET channelincluding the first semiconductor material; and (iii) a second MOSFETdisposed on the substrate and including a second MOSFET channel disposedin a portion of the second semiconductor layer over a second insulatingmaterial, the second MOSFET channel including the second semiconductormaterial.

The first and second MOSFETs are at least partially depleted duringoperation. Moreover, the first MOSFET and/or the second MOSFET may befully depleted during operation. Each of the first and second MOSFETsmay be an nMOSFET or a pMOSFET.

The first and/or semiconductor material may include or consist of agroup IV material, a III-V material, and/or a II-VI material. Specificexamples of such materials include silicon, SiGe, germanium, an array ofcarbon nanotubes, and mixtures or alloys thereof; and gallium arsenide,indium arsenide, indium gallium arsenide, indium phosphide, galliumnitride, indium antimonide, gallium antimonide, gallium phosphide, andmixtures or alloys thereof. At least one of the first and secondsemiconductor materials may be tensilely strained and/or compressivelystrained.

The first semiconductor layer may have a first crystalline orientation,the second semiconductor layer may have a second crystallineorientation, and the first crystalline orientation may be different fromthe second crystalline orientation. The first crystalline orientationmay be selected from a {100} family of crystalline planes; the secondcrystalline orientation may be selected from a {110} family ofcrystalline planes.

The first semiconductor layer may have a first crystalline in-planerotation, the second semiconductor layer may have a second crystallinein-plane rotation different from the first crystalline in-planerotation.

A crystallographic orientation of the nMOSFET channel may be parallel toa crystallographic direction selected from any of a <110> family ofcrystallographic directions. A crystallographic orientation of thepMOSFET channel is parallel to a crystallographic direction selected anyof a <100> family of crystallographic directions.

An insulator layer including the first and second insulating materialmay be disposed over the semiconductor substrate, with the firstinsulating material being identical or substantially similar to thesecond insulating material.

A first insulator layer including the first insulating material may bedisposed over at least the first portion of the substrate, and a secondinsulator layer including the second insulator material may be disposedover at least the second portion of the substrate, such that the firstMOSFET channel is disposed over the first insulator layer, and thesecond MOSFET channel is disposed over the second insulator layer.

The first semiconductor layer may be disposed over a region of thesecond semiconductor layer, with the first semiconductor layer having afirst type of strain and a first lattice constant, and the secondsemiconductor layer having a second type of strain and the first latticeconstant. Each of the first and second types of strain may be either oftensile or compressive strain.

The first semiconductor layer may have a first type of strain and afirst lattice constant, and the second semiconductor layer may bedisposed over a region of the first semiconductor layer, the secondsemiconductor layer having a second type of strain and the first latticeconstant.

The first MOSFET may include a first gate dielectric layer (including afirst dielectric material) disposed over the first MOSFET channel andthe second MOSFET may include a second gate dielectric layer (includinga second dielectric material) disposed over the second MOSFET channel.The first and second dielectric materials may be identical,substantially similar or substantially different. The first and/or thesecond dielectric material may include or consist of at least one ofsilicon dioxide, silicon oxynitride, silicon nitride, barium oxide,strontium oxide, calcium oxide, tantalum oxide, titanium oxide,zirconium oxide, hafnium oxide, aluminum oxide, lanthanum oxide, yttriumoxide, yttrium aluminate, lathanum aluminate, lanthanum silicate,yttrium silicate, hafnium silicate, zirconium silicate, and dopedalloys, undoped alloys, mixtures, and/or multilayers thereof.

The first MOSFET may include a first gate electrode layer comprising afirst conductive material disposed over the first MOSFET channel, andthe second MOSFET may include a second gate electrode layer comprising asecond conductive material disposed over the second MOSFET channel. Thefirst and second conductive materials may be identical, substantiallysimilar or substantially different.

The first and/or second conductive material may include at least one ofdoped polycrystalline silicon, doped polycrystalline SiGe, Al, Ag, Bi,Cd, Fe, Ga, Hf, In, Mn, Nb, Y, Zr, Ni, Pt, Be, Ir, Te, Re, Rh, W, Mo,Co, Fe, Pd, Au, Ti, Cr, Cu, and doped alloys, undoped alloys, mixtures,and/or multilayers thereof.

A portion of the first semiconductor layer may be disposed over thesecond portion of the substrate, and the second semiconductor layer maybe disposed over the portion of the first semiconductor layer.

A portion of the second semiconductor layer may be disposed over thefirst portion of the substrate and the first semiconductor layer may bedisposed over the portion of the second semiconductor layer.

The first insulator layer and/or second insulator layer may include acrystalline oxide layer, which may induces a strain in the first andsecond semiconductor layers. The crystalline oxide layer may include atleast one of a multicomponent metal oxide and a dielectric materialhaving a lattice constant of approximately 5.4 Å and a body-centeredcubic structure.

The multicomponent metal oxide may include or consist of one or moremetals selected from the group consisting of Al, Ti, Zr, Hf, V, Nb, Ta,Cr, Mo, W, and Cu. The multicomponent metal oxide may include or consistof at least one of barium strontium titanate, barium strontiumzirconate, barium strontium hafnate, lead titanate, yttrium aluminate,lanthanum aluminate, lead zirconium titanate, hafnium silicate,zirconium silicate, strontium silicon oxide, zirconium silicon oxide,hafnium silicon oxide, hafnium oxide, zirconium oxide, strontiumtitanate, lanthanum oxide, yttrium oxide, titanium oxide, bariumtitanate, lanthanum aluminate, lanthanum scandium oxide, and/or aluminumoxide. The dielectric material may include or consist of at least one ofcesium oxide, aluminum nitride, and lanthanum aluminum oxide.

The first insulator layer may include or consist of a first crystallineoxide that induces a first type of strain in the first semiconductorlayer, and the second insulator layer may include a second crystallineoxide that induces a second type of strain in the second semiconductorlayer.

The first insulator layer may induce a first strain in the firstsemiconductor layer, and the second insulator layer induces a secondstrain in the second semiconductor layer.

In another aspect, the invention features a method for forming astructure, the method including the steps of (i) providing asemiconductor substrate, (ii) defining a first portion of the substrate;(iii) defining a second portion of the substrate; (iv) providing a firstinsulating material over the first portion of the substrate; (v)providing a second insulating material over the second portion of thesubstrate; (vi) forming a first semiconductor layer including a firstsemiconductor material over at least the first portion of the substrate;(vii) forming a second semiconductor layer including a secondsemiconductor material over at least the second portion of thesubstrate; (viii) forming a first MOSFET on the substrate, the firstMOSFET including a first MOSFET channel disposed in a portion of thefirst semiconductor layer over the first insulating material, the firstMOSFET channel including the first semiconductor material; and (ix)forming a second MOSFET on the substrate, the second MOSFET including asecond MOSFET channel disposed in a portion of the second semiconductorlayer over the second insulating material, the second MOSFET channelincluding the second semiconductor material. The first and secondMOSFETs are at least partially depleted during operation.

Defining the first and second portions of the substrate may includedefining a shallow trench isolation region. The first insulatingmaterial may be identical to or substantially the same as the secondinsulating material and providing the first and second insulatingmaterials may include forming an insulator layer over the substrate.

Forming the first semiconductor layer may include bonding the firstsemiconductor layer to the insulator layer. The first semiconductorlayer may be formed over the first and second portions of the substrateand the second semiconductor layer may be formed over a second portionof the first semiconductor layer disposed over the second portion of thesubstrate. The second portion of the first semiconductor layer may bethinned prior to forming the second semiconductor layer. Forming theinsulator layer, the first semiconductor layer, and/or the secondsemiconductor layer over the substrate may involve deposition.

Either of the first MOSFET or second MOSFET may be an nMOSFET or apMOSFET.

The first semiconductor layer may be formed over the first and secondportions of the substrate. The second semiconductor layer may be formedover the first semiconductor layer.

A portion of the second semiconductor layer disposed over the firstsemiconductor layer over the first portion of the substrate may beremoved.

A regrowth layer may be formed over the first semiconductor layerdisposed over the first portion of the substrate.

Forming the regrowth layer may include providing additional firstsemiconductor material and a total thickness of the first semiconductorlayer and the regrowth layer may be approximately the same as a totalthickness of the first semiconductor layer and the second semiconductorlayer in a second portion of the substrate.

Providing the first and second insulating materials may involvedeposition, and the first insulating material may be different from thesecond insulating material. Forming the first and second semiconductorlayers may involve deposition, and the first semiconductor material maybe substantially the same as or different from the second semiconductormaterial. At least one of the first and second insulating materials mayinclude a crystalline oxide.

The first semiconductor layer may have a thickness selected from a rangeof 1-50 nm. The second semiconductor layer may have a thickness selectedfrom a range of 1-50 nm. For particularly aggressive FDSOI devices, thefirst and/or second semiconductor layer may have a thickness morepreferably selected from a range of 1-20 nm, or more preferably 1-10 nm.

In another aspect, the invention features a substrate having aninsulator layer disposed thereon, and a FinFET disposed over thesubstrate. The FinFET includes (i) a source region and a drain regiondisposed in contact with the insulator layer; (ii) at least one finextending between the source and the drain regions and comprising abilayer; (iii) a gate disposed above the bilayer, extending over atleast one fin and between the source and the drain regions; and a gatedielectric layer disposed between the gate and the fin.

The bilayer may include a second semiconductor material disposed over afirst semiconductor material. The first semiconductor material and thesecond semiconductor material may be the same or different, and each mayinclude or consist of a group IV material, a III-V material, and/or aII-VI material. The group IV material may be silicon, SiGe, germanium,an array of carbon nanotubes, and/or mixtures or alloys thereof. TheIII-V material may be gallium arsenide, indium arsenide, indium galliumarsenide, indium phosphide, gallium nitride, indium antimonide, galliumantimonide, gallium phosphide, and/or mixtures or alloys thereof.

At least one of the first and second semiconductor materials may betensilely strained or compressively strained. The gate dielectric may bedisposed proximate the first semiconductor material and the secondsemiconductor material.

In another aspect, the invention comprises a structure including asubstrate having a crystalline oxide layer disposed thereon, and aFinFET disposed over the substrate. The FinFET includes (i) a sourceregion and a drain region disposed in contact with the insulator layer;(ii) at least one fin extending between the source and the drainregions, the fin comprising a first semiconductor layer disposed overthe crystalline oxide layer; (iii) a gate disposed above the firstsemiconductor layer, extending over at least one fin and between thesource and the drain regions; and (iv) a gate dielectric layer disposedbetween the gate and the fin.

In another aspect, the invention comprises a structure including (i) asubstrate; (ii) a first insulator layer disposed over at least a firstportion of the substrate; (iii) a second insulator layer disposed overat least a second portion of the substrate; (iv) a first FinFET disposedover the substrate; and (v) a second FinFET disposed over the substrate.The first FinFET includes (i) a first source region and a first drainregion disposed over and in contact with the first insulator layer; (ii)a first fin extending between the first source and the first drainregions, the first fin including a first semiconductor material disposedon at least one vertically oriented sidewall of the first fin; (iii) afirst gate disposed above the substrate, extending over the first finand between the first source and the first drain regions; and (iv) afirst gate dielectric layer disposed between the first gate and thefirst fin. The second FinFET includes (i) a second source region and asecond drain region disposed over and in contact with the secondinsulator layer; (ii) a second fin extending between the second sourceand the second drain regions, the second fin including a secondsemiconductor material disposed on at least one vertically orientedsidewall of the second fin; (iii) a second gate disposed above thesubstrate, extending over the second fin and between the second sourceand the second drain regions; and (iv) a second gate dielectric layerdisposed between the second gate and the second fin. The firstsemiconductor material has a first crystalline orientation, the secondsemiconductor material has a second crystalline orientation thatpreferably differs from the first crystalline orientation.

The first insulator layer may include a first crystalline oxide, thesecond insulator layer may include a second crystalline oxide, the firstfin may include the first crystalline oxide, and the second fin mayinclude the second crystalline oxide.

The first crystalline oxide and the second crystalline oxide may besubstantially different. The first fin and second fin may besubstantially parallel. The first semiconductor material and the secondsemiconductor material may be substantially the same. The firstcrystalline orientation may be selected from a {100} family ofcrystalline planes or a {110} family of crystalline planes. The firstFinFET may include an n-channel device and the second FinFET comprises ap-channel device.

In another aspect, the invention features a method for forming astructure, the method including (i) providing a substrate having aninsulator layer disposed thereon, and a bilayer disposed in contact withthe insulator layer, the bilayer including a second semiconductor layerdisposed over a first semiconductor layer; and (ii) forming a FinFET onthe substrate. The FinFET is formed by (i) patterning the bilayer todefine a source region, a drain region, and at least one fin disposedbetween the source and the drain regions, (ii) forming a gate dielectriclayer, at least a portion of the gate dielectric layer being disposedover the fin, and (iii) forming a gate over the gate dielectric layerportion disposed over the fin.

The bilayer may include or consist of at least one of a group II, agroup III, a group IV, a group V, or a group VI element. The bilayer mayinclude a strained semiconductor layer that may be tensilely strained orcompressively strained.

In another aspect, the invention features a structure including (i) asubstrate; (ii) a first FinFET disposed over the substrate; and (iii) asecond FinFET disposed over the substrate. The first FinFET includes afirst semiconductor material having a first crystalline orientation, thesecond FinFET includes a second semiconductor material having a secondcrystalline orientation, and the first and second crystallineorientations are different.

In another aspect, the invention features a method for forming astructure, the method including providing a substrate having aninsulator layer disposed thereon, and a first semiconductor layerdisposed in contact with the insulator layer; and forming a FinFET onthe substrate. The FinFET may be formed by (i) patterning the firstsemiconductor layer to define a source region, a drain region, and atleast one fin disposed between the source and the drain regions, (ii)selectively depositing a second semiconductor layer over a top surfaceof at least one fin to form a bilayer, (iii) forming a gate dielectriclayer, at least a portion of the gate dielectric layer being disposedover the fin, and (iv) forming a gate over the gate dielectric layerportion disposed over the fin.

In another aspect, the invention features a method for forming astructure, the method including providing a substrate having acrystalline oxide layer disposed thereon, and a first semiconductorlayer disposed in contact with the crystalline oxide layer; and forminga FinFET on the substrate. The FinFET is formed by (i) patterning thefirst semiconductor layer to define a source region, a drain region, andat least one fin disposed between the source and the drain regions, (ii)forming a gate dielectric layer, at least a portion of the gatedielectric layer being disposed over the fin, and (iii) forming a gateover the gate dielectric layer portion disposed over the fin.

In another aspect, the invention features a method for forming astructure, the method including (i) providing a substrate having a firstsemiconductor layer disposed thereon; (ii) defining a fin in the firstsemiconductor layer, the fin having an aspect ratio; and (iii) removingtop portion of the fin, and thereafter selectively depositing a secondsemiconductor layer over the top portion of the fin so as to preservethe aspect ratio of the fin.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1-15 are a series of schematic cross-sectional views of severalalternative semiconductor structure illustrating processes forfabricating the structures; and

FIGS. 16-33C are schematic cross-sectional and top views of substratesillustrating a method for fabricating a FinFET.

Like-referenced features represent common features in correspondingdrawings.

DETAILED DESCRIPTION

Referring to FIG. 1, a semiconductor-on-insulator substrate (SOI) 100includes a semiconductor substrate 110 that itself includes or consistsof a semiconductor material, such as silicon, germanium, SiGe, siliconcarbide, gallium arsenide, indium phosphide, and/or gallium nitride. Aninsulator layer 120, e.g., a continuous buried insulating layer, isdisposed over the semiconductor substrate 110. Insulator layer 120 mayinclude or consist of, for example, silicon dioxide (SiO₂), siliconnitride (Si₃N₄ or other compositions), aluminum oxide, magnesium oxide,and/or other dielectric materials, or may be a multilayer structureincluding one or more different materials. The insulator layer 120 mayhave a thickness t₀ of, e.g., 50-200 nanometers (nm). For highly scaleddevices, e.g., devices with gate lengths shorter than 100 nm, theinsulator layer 120 may be relatively thin, i.e., have a thickness toof, e.g., 10-50 nm for better control of short channel effects. In anembodiment, SOI substrate 100 may include a single insulating substrate(not shown), rather than the combination of semiconductor substrate 110and insulator layer 120. The single insulating substrate may be formedfrom an insulating material such as SiO₂, silicon nitride, glass,aluminum oxide, an organic polymer, plastic, or some combination ofmaterials.

The SOI substrate may be a commercially available substrate that may beobtained from, e.g., SOITEC Silicon on Insulator Technologies of Bernin,France.

A first semiconductor layer 130 is disposed over the insulator layer120. The first semiconductor layer 130 may include or consist of a firstsemiconductor material suitable for use as a channel of a MOSFET, suchas at least one of a group IV material, e.g., silicon, SiGe, germanium,or an array of carbon nanotubes; a III-V material such as galliumarsenide, indium arsenide, indium gallium arsenide, indium phosphide,gallium nitride, indium antimonide, gallium antimonide, galliumphosphide; or a II-VI material, and mixtures or alloys including one ormore of the aforementioned materials. The first semiconductor layer 130may be strained, including tensilely or compressively strained, e.g.,tensilely or compressively strained silicon. In some embodiments, thefirst semiconductor layer 130 may include approximately 100% Ge, and maybe compressively strained. The first semiconductor layer 130 may have aninitial thickness t₁ of, e.g., 1-50 nm, more preferably 1-20 nm forfully depleted devices, most preferably 1-10 nm or even 1-5 nm.

The first semiconductor layer 130 may initially be formed on a handlewafer (not shown) and then bonded to the insulator layer 120. Forexample, a handle wafer may include a Si_(1-x)Ge_(x) layer with x>0. Asilicon layer formed over this Si_(1-x)Ge_(x) layer will be tensilelystrained, and remains tensilely strained after being bonded to theinsulator layer 120 to form the first semiconductor layer 130. Agermanium layer formed over this Si_(1-x)Ge_(x) layer will becompressively strained, and remains compressively strained after beingbonded to the insulator layer 120 to form the first semiconductor layer130. Alternatively, strain in the first semiconductor layer may arisefrom mechanical deformation of the handle wafer or from thermal mismatchwith the handle wafer. For example, the handle wafer may be mechanicallybiaxially or uniaxially strained by bending or heated to elevatedtemperature prior to bonding to insulator layer 120. After the handlewafer is removed, first semiconductor layer 130 will remain strained.See, for example, U.S. Ser. No. 10/456,103, filed Jun. 6, 2003,incorporated herein in its entirety.

A conductive layer (not pictured) may be disposed beneath insulatorlayer 120. This conductive layer may be used in subsequently formeddevices as a ground plane or as a second gate in, e.g., in a planardouble-gate transistor. This conductive layer may include the samematerial as may be used for a gate electrode, e.g., dopedpolycrystalline silicon, doped polycrystalline SiGe, Al, Ag, Bi, Cd, Fe,Ga, Hf, In, Mn, Nb, Y, Zr, Ni, Pt, Be, Ir, Te, Re, Rh, W, Mo, Co, Fe,Pd, Au, Ti, Cr, Cu, and doped or undoped alloys, or mixtures ormultilayers thereof.

During device fabrication, a first portion 140 of the substrate 100 anda second portion 150 of the substrate 100 may be defined as shown inFIG. 2. The first and second substrate portions 140, 150 may be definedby, e.g., the formation of a shallow trench isolation (STI) region 160.The STI region 160 may be formed by methods known in the art, e.g., asdescribed in co-pending U.S. Ser. No. 10/794,010, publication No.2004/0173812 Al, incorporated by reference herein in its entirety.

A first MOSFET may be fabricated on the first portion 140 of thesubstrate 100 and a second MOSFET may be fabricated on the secondportion 150 of the substrate 100 as follows. After STI 160 has beendefined, a first portion 170 of the first semiconductor layer 130disposed over the first portion of the substrate 100 may covered by amask 180. The mask 180 may be formed from a masking material selected tobe stable during the formation of a second layer comprising a secondmaterial over the second portion of the substrate. Moreover, the maskingmaterial is selected such that it may be selectively removed withrespect to the second semiconductor layer, as described below. Themasking material may include or consist of a dielectric material, suchas silicon dioxide, silicon oxynitride, or silicon nitride.

In an embodiment, the first MOSFET is an nMOSFET and the second MOSFETmay be a pMOSFET. In another embodiment, the first MOSFET is a pMOSFETand the second MOSFET may be an nMOSFET. In yet another embodiment, boththe first and second MOSFETs are both nMOSFETs or pMOSFETs.

Mask 180 may be defined after the completion of STI formation.Alternatively, mask 180 may include masking material used to protectthose regions of the first semiconductor layer that are not removedduring STI formation; after STI formation, the masking material may beselectively removed from the second portion of the substrate where thepMOSFET will be formed, thereby exposing the portion of the firstsemiconductor layer disposed over the second portion of the substrate.Masking material used during STI formation may be, for example, asilicon nitride chemical-mechanical polishing (CMP) stop layer 182disposed over a pad oxide layer 184.

Referring to FIG. 2 as well as to FIG. 3, a second semiconductor layer200 may be formed over an exposed surface of a second portion 210 of thefirst semiconductor layer 130 that is disposed over the second portion150 of the substrate 100. The second semiconductor layer 200 may includeor consist of a material suitable for use as a channel of a MOSFET,e.g., a group IV material such as silicon, SiGe, germanium, or an arrayof carbon nanotubes; a III-V material such as gallium arsenide, indiumarsenide, indium gallium arsenide, indium phosphide, gallium nitride,indium antimonide, gallium antimonide, or gallium phosphide; and a II-VImaterial, or mixtures or alloys including one or more of theaforementioned materials. The second semiconductor layer 200 may bestrained, including tensilely or compressively strained, e.g., tensilelyor compressively strained silicon.

The second semiconductor layer 200 may be formed by a depositionprocess, such as chemical-vapor deposition (CVD) or atomic layerdeposition (ALD). CVD includes the introduction of multiple reagentsinto a reactor simultaneously. ALD includes the sequential introductionof multiple reagents into a reactor, including, but not limited to,atomic layer epitaxy, digital chemical vapor deposition, pulsed chemicalvapor deposition, and other like methods.

A thickness t₂ of the second semiconductor layer 200 may be selected tobe thick enough to enable carrier conduction, e.g., in the channel of asubsequently formed transistor, while preferably thin enough to supportfully depleted device operation. The second semiconductor layer 200 mayhave a thickness t₂ of, e.g., 1-50 nm, more preferably 1-20 nm, mostpreferably 1-10 nm or even 1-5 nm for fully depleted devices.

In some embodiments, a total thickness t₃ of the first semiconductorlayer 130 initial thickness t₁ and the second semiconductor layerthickness t₂ may be too great to allow fully depleted operation ofdevices formed on the second semiconductor layer 200. It may beadvantageous, therefore, to reduce the initial thickness t₁ of at leastthat portion of the first semiconductor layer 130 disposed over thesecond portion 150 of the substrate, prior to the formation of thesecond semiconductor layer 200. The initial thickness t₁ of the firstsemiconductor layer 130 may be selectively reduced over the secondportion 150 of the substrate by etching, e.g., by reactive ion etching(RIE) or by an in-situ etch prior to deposition in the deposition tool.For example, in an embodiment in which the first semiconductor layer 130is silicon, the exposed portion 210 of the first semiconductor layer maybe thinned in a chlorine-containing ambient including, e.g., hydrogenchloride or chlorine, to a reduced thickness t₄ of, e.g., 1-10 nm. Thereduced thickness t₄ is thin enough such that the total thickness t₃ ofreduced thickness t₄ and second semiconductor layer thickness t₂ willenable fully depleted device operation. The reduced thickness t₄ may bethick enough such that the remaining portion of the first semiconductorlayer 130 does not agglomerate during subsequent thermal processingprior to and including the deposition of second semiconductor layer 200.Subsequently, the second semiconductor layer 200 may be deposited overthe exposed portion 210 of the first semiconductor layer 130, such thatthe total thickness t₃ of the second semiconductor layer 200 and thethinned first semiconductor layer 130 is less than 50 nm, i.e., asufficiently small thickness for the formation of fully depleteddevices. In some embodiments, the total thickness t₃ of the reducedfirst semiconductor layer 130 thickness t₄ and the second semiconductorlayer 200 thickness t₂ may be approximately the same as t₁, i.e., theinitial thickness of the first semiconductor layer 130.

In practice, the total thickness t₃ of the first semiconductor layer 130and the second semiconductor layer 200 is preferably 0.25 to 0.7 times agate length of a transistor to be formed over the first and secondsemiconductor layers 130, 200. If the portion of the first semiconductorlayer 130 disposed over the second portion of the substrate iscompletely removed, the thickness t₂ of the second semiconductor layer200 may be 0.25 to 0.7 times a gate length of a transistor formed solelyover the second semiconductor layer 200. Similarly, in a transistorformed solely over the first semiconductor layer 130, the initialthickness t₁ of the first semiconductor layer preferably may be 0.25 to0.7 times a gate length of that transistor. Selection of a semiconductorlayer thickness in the range of 0.25 to 0.7 times a transistor gatelength may be preferable for improved operation of the transistor, asthis relationship between the semiconductor layer thickness and thetransistor gate length may enable fully depleted behavior in thetransistor.

In an embodiment, the first semiconductor layer 130 includes relaxedsilicon. A compressively strained second semiconductor layer 200 may beformed by thinning the first semiconductor layer 130 and depositing thesecond semiconductor layer 200 such that the second semiconductor layer200 includes compressively strained SiGe.

In another embodiment, the first semiconductor layer 130 includesstrained silicon. To obtain a compressively strained secondsemiconductor layer 200, the first semiconductor layer 130 may bethinned and the second semiconductor layer 200 deposited, the secondsemiconductor layer 200 including compressively strained Si_(1-x)Ge_(x)material having a Ge content x greater than that of the Si_(1-x)Ge_(x)of a handle wafer over which the first semiconductor layer 130 has beenformed.

More generally, a compressively strained second semiconductor layer 200may be formed from a material having a relaxed lattice constant greaterthan the strained lattice constant to which the first semiconductorlayer 130 is strained, i.e., the second semiconductor material may havea relaxed lattice constant greater than that of the handle wafer onwhich the first semiconductor layer has been formed (and which inducedstrain in the first semiconductor layer). The deposition of such asecond semiconductor material on the tensilely strained firstsemiconductor layer will cause the second semiconductor layer 200 to becompressively strained to the same lattice constant to which the firstsemiconductor layer 130 is strained.

As an example, consider the lattice constants of three differentmaterials. The lattice constant of relaxed silicon is less than thelattice constant of relaxed Si_(0.5)Ge_(0.5), which is less than thelattice constant of relaxed germanium. Strained silicon grown on relaxedSi_(0.5)Ge_(0.5) will have a lattice constant of the relaxedSi_(0.5)Ge_(0.5) and will be tensilely strained. Strained germaniumgrown on relaxed Si_(0.5)Ge_(0.5) will also have the lattice constant ofthe relaxed Si_(0.5)Ge_(0.5), but will be compressively strained.Therefore, if the first semiconductor layer is substantially 100%strained silicon with the lattice constant of relaxed Si_(0.5)Ge_(0.5),the second semiconductor layer, in order to be compressively strained,has a lattice constant greater than that of relaxed Si_(0.5)Ge_(0.5).

In an alternative embodiment, the first semiconductor layer 130 may be acompressively strained germanium layer suitable for the formation of apMOSFET. Then, the first semiconductor layer 130 may be thinned over afirst portion 140 of the substrate 100 over which an nMOSFET will beformed. The second semiconductor material may include a materialsuitable for use as the channel of an nMOSFET, such as a group IVmaterial, e.g., silicon, SiGe, germanium, or an array of carbonnanotubes; a III-V material such as gallium arsenide, indium arsenide,indium gallium arsenide, indium phosphide, gallium nitride, indiumantimonide, gallium antimonide, or gallium phosphide; or a II-VImaterial, and mixtures or alloys including one or more of theaforementioned materials.

Referring to FIG. 4, a gate dielectric layer 220 may be formed over thefirst and second semiconductor layers 130, 200 by, e.g., deposition orgrowth. The gate dielectric layer 220 may be formed by one or more of anumber of techniques, such as molecular beam epitaxy (MBE), oxidation,nitridation, CVD, ALD, or a combination of these or other methods. Thegate dielectric layer may include or consist of a dielectric materialsuch as, for example, silicon dioxide (SiO₂), silicon oxynitride(SiO_(x)N_(y)), silicon nitride (Si₃N₄ or other compositions), bariumoxide (BaO), strontium oxide (SrO), calcium oxide (CaO), tantalum oxide(Ta₂O₅), titanium oxide (TiO₂), zirconium oxide (ZrO₂), hafnium oxide(HfO₂), aluminum oxide (Al₂O₃), lanthanum oxide (La₂O₃), yttrium oxide(Y₂O₃), yttrium aluminate, lathanum aluminate, lanthanum silicate,yttrium silicate, hafnium silicate, zirconium silicate, and doped orundoped alloys, mixtures or multilayers, thereof.

Alternatively, the first and second gate dielectric layers may includefirst and second dielectric materials that are identical orsubstantially similar. Essentially, a single gate dielectric layer 220may be utilized over the first and second substrate regions 140, 150.

A gate electrode layer 230 may be formed over the gate dielectric layerby, e.g., CVD or ALD, and subsequently patterned to define a gate. Thegate electrode layer 230 may include or consist of a suitably conductivematerial such as, for example, doped polysilicon, doped polycrystallineSiGe, Al, Ag, Bi, Cd, Fe, Ga, Hf, In, Mn, Nb, Y, Zr, Ni, Pt, Be, Ir, Te,Re, Rh, W, Mo, Co, Fe, Pd, Au, Ti, Cr, Cu, and doped or undoped alloys,mixtures or multilayers thereof. Gate electrode layers of differentmaterials and/or compositions may be utilized over the first and secondsubstrate regions 140, 150, i.e., a first electrode layer including afirst conductive material may be formed over the first substrate region140, a second electrode layer including a second conductive material maybe formed over the second substrate region 150, and the first and secondconductive materials may be substantially different.

Alternatively, the first gate electrode layer may include a firstconductive material, the second gate dielectric layer may include asecond conductive material, and the first and second conductivematerials may be identical or substantially similar. Essentially, asingle gate electrode layer 230 may be utilized over both first andsecond substrate regions.

The use of two different channel materials may facilitate the use of asingle midgap metal gate for nMOSFET and pMOSFET devices, e.g., a gateelectrode having a workfunction between that of n⁺ polysilicon(approximately 4.2 eV) and p⁺ polysilicon (approximately 5.2 eV) andpreferably approximately 4.4-4.9 eV, such as titanium nitride (TiN),tantalum nitride (TaN), tantalum silicon nitride (TaSiN), tungsten (W),molybdenum (Mo), titanium (Ti), tantalum (Ta), polycrystalline carbon(C), or silicides of nickel or other metals (e.g., NiSi), thus makingdevice fabrication less complex in comparison to the use of twodifferent gate electrodes.

Portions of the gate electrode layer 230 and gate dielectric layer 220may be removed as shown in FIGS. 4 and 5 by, e.g., etching to definefirst and second gate electrodes 240 a, 240 b disposed over the firstand second semiconductor layers 130, 200, respectively. Sidewall spacers250 may be defined proximate the gate electrodes 240 a, 240 b. Sourceand drain regions 260 may be formed for nMOSFET and pMOSFET devices by,e.g., implanting or diffusing appropriate dopants proximate the gateelectrodes 240 a, 240 b, as is known in the art.

The source and drain regions 260 may also include a semiconductormaterial (which may be different from the semiconductor materialdisposed in nMOSFET channel 270 a and pMOSFET channel 270 b) defined inthe first and second semiconductor layers 130, 200, respectively,beneath the gate electrodes 240 a, 240 b. Such a source/drain materialmay be formed by deposition (e.g., CVD or ALD), which may be preceded byan etch that removes at least some of the preexisting material presentin the source and drain regions 260. The source/drain material mayinduce strain in the device channels 270 a, 270 b because of adifference in lattice constant and/or coefficient of thermal expansionbetween the source/drain material and the channel materials disposedbeneath the gate electrodes 240 a, 240 b. The source/drain material mayalso serve to decrease series or contact resistance in the nMOSFET andpMOSFET devices. The source/drain material may also enable silicidationof the source and drain regions, as the initial thickness t₁ of firstsemiconductor layer 130 and/or thickness t₃ (the reduced thickness t₄ ofthe first semiconductor layer 130 in addition to thickness t₂ of secondsemiconductor layer 200) present in the source and drain regions may notbe sufficient to enable formation of a low-resistivity silicide.

A self-aligned silicide (salicide) may be formed in source and drainregions 260 and optionally on top of first and second gate electrodes240 a, 240 b as follows. A conductive layer is formed over the substrate100. For example, a metal such as titanium, platinum, zirconium, cobalt,nickel, or alloys, mixtures, or multilayers thereof is deposited by,e.g., CVD or sputtering, with the conductive layer having a thicknessof, e.g., 50-200 Å. In some embodiments, additional semiconductormaterial is formed over source and drains 260 regions, and optionallyover the gate electrodes 240 a, 240 b, prior to the formation of theconductive layer, to define raised source and drain regions. An annealis performed to react the conductive layer with source and drain regions260 and optionally with tops of first and second gate electrodes 240 a,240 b. Anneal parameters may be, for example, 400-800° C. for 1-120seconds. Unreacted portions of the conductive layer disposed directlyover insulator material, such as sidewall spacers 250, are removed by achemical strip. A suitable chemical strip is a solution includingH₂SO₄:H₂O₂ at a ratio of 3:1. A second anneal may be performed tofurther lower resistivity of the salicide. The second anneal parametersmay be, for example, 600-900° C. for 1-120 seconds.

An nMOSFET 280 includes channel 270 a disposed in a portion of the firstsemiconductor layer 130 over a first insulating material 120 a, suchthat the nMOSFET channel 270 a includes the first semiconductormaterial. A pMOSFET 290 includes channel 270 b disposed in a portion ofthe second semiconductor layer 200 over a second insulating material 120b, such that the pMOSFET channel 270 b includes the second semiconductormaterial. In some embodiments, insulator layer 120 including the firstand second insulating materials is disposed across the semiconductorsubstrate 110, and the first and second insulating materials may beidentical or substantially similar. In other embodiments, a firstinsulator layer including the first insulating material is disposed overa first portion of the semiconductor substrate 110, a second insulatorlayer including the second insulating material is disposed over a secondportion of the semiconductor substrate 110, and the first and secondinsulating materials are substantially different. This embodiment isdescribed in greater detail with respect to FIGS. 12-15.

The channels of the nMOSFET and pMOSFET may include one or more channeldopants, e.g., boron, arsenic, antimony, phosphorous, or indium. Suchchannel dopants may be of a type opposite the dopant type present in thesource and drain regions of a particular device, and may influencecontrol of the device threshold voltage. For example, the nMOSFET mayinclude arsenic doping in the source and drain regions and boron in thechannel region. These dopants may be present at a fairly low level,e.g., at a level less than 10¹⁶-10¹⁷ cm⁻³. In an embodiment, thesechannel dopants may be present at a level less than 10¹⁵ cm⁻³.

In some embodiments, the nMOSFET and the pMOSFET devices 280, 290 havedifferent gate dielectric compositions and/or different gate electrodecompositions. This may be achieved by the utilization of gate dielectriclayers of different materials and/or compositions over the first andsecond substrate regions 140, 150, i.e., a first dielectric layer 220 aincluding a first dielectric material may be disposed over the firstsubstrate region 140, a second dielectric layer 220 b including a seconddielectric material may be disposed over the second substrate region150, and the first and second dielectric materials may be substantiallydifferent. Two different types of dielectric layers 220 a, 220 b andgate electrode layers may be formed by the use of a “dummy gate”process. Here, the nMOSFET and pMOSFET devices 280, 290 are formed asdescribed above, with the use of single gate dielectric layer 220. Afterthe formation of sidewall spacers 250, a thick oxide layer may be formedover the nMOSFET and pMOSFET devices 280, 290 and planarized by, e.g.,CMP, to expose top portions of the first and second gate electrodes 240a, 240 b. A mask may be formed over, e.g., the nMOSFET device 280 toprotect the gate electrode 240 a. The gate electrode 240 b and theunderlying gate dielectric material of the pMOSFET 290 may be removedby, e.g., a wet etch. A second gate dielectric layer 220 b including asecond dielectric material and a second gate electrode 240 b may bedefined for the pMOSFET 290. The second dielectric material may besubstantially different from the first dielectric material. The secondgate electrode material may be substantially different from the firstgate electrode material. A second planarization step may be performed toremove residual materials such as masks, as well as portions of thesecond gate dielectric material and second gate electrode material thatare not needed for the second gate dielectric layer and the second gateelectrode. Finally, the thick oxide is removed by, e.g., a wet etch.

As used herein, a “fully depleted” SOI device is fully depleted betweenthe channel and the underlying insulating layer when the gate voltage isequal to the device's threshold voltage. The region between the channeland the underlying insulating layer is considered to be fully depletedif it is substantially free of charge carriers. The nMOSFET may be fullydepleted during operation, and the pMOSFET may be fully depleted duringoperation.

During device operation, both the nMOSFET and the pMOSFET may havesimilar body thicknesses, i.e., similar total thicknesses of layersdisposed beneath the gate, and both device types may have carrierdepletion regions beneath the respective channels that extend to theunderlying insulator layer.

Partially depleted on-insulator devices may be formed over particularregions of the substrate by modification of the above technique. Morespecifically, the body thickness, i.e., the thickness of the first orsecond semiconductor layers, may be sufficiently increased for certaindevices to allow partially depleted operation. As used herein, a“partially depleted” SOI device is not fully depleted between thechannel and the underlying insulating layer when the gate voltage isequal to the device's threshold voltage. When a region is not fullydepleted, it is not substantially free of charge carriers.

An alternative starting material may be used to form the semiconductorstructure having a first material disposed over a first portion of thesubstrate and a second material disposed over a second portion of thesubstrate, as illustrated in FIG. 3. A bilayer semiconductor layerstructure 300 may be formed over the insulator layer 120 disposed onsubstrate 110 as shown in FIG. 6. This bilayer 300 includes firstsemiconductor layer 130 and second semiconductor layer 200 disposed overthe first semiconductor layer 130. The second semiconductor layer 200may include any material particularly suitable for either nMOSFET orpMOSFET operation. For example, for use in a pMOSFET device, the bilayerstructure may be thin, having a total thickness t₅ of, e.g., 1-50 nm.The second semiconductor layer 200 may be any material suitable for useas a channel of a pMOSFET and may include, e.g., unstrained or strainedgermanium. The second semiconductor layer 200 may constitute themajority of the thickness of the bilayer 300. The underlying firstsemiconductor layer 130 may include any material suitable for use as achannel of an nMOSFET, e.g., unstrained or strained silicon.

The presence of a thin first semiconductor layer under the secondsemiconductor layer in a pMOSFET will not disturb operation of thepMOSFET, and may serve as a template for epitaxial formation of athicker regrowth layer including the first semiconductor material, asdescribed below, for use as a channel of an nMOSFET.

First and second portions 140, 150 of the substrate 100 may be definedas shown in FIG. 7 by, e.g., the formation of STI region 160, asdescribed above with reference to FIG. 2.

After STI 160 has been defined, a first portion 310 of the secondsemiconductor layer 200 may be exposed while a second portion 320 of thesecond semiconductor layer 200 (disposed over the second portion 150 ofthe substrate 100) is covered by mask 180. The mask 180 may be formedfrom a masking material selected such that the material is stable duringthe removal of the first portion 310 of the second semiconductor layer200 and the formation of a regrowth layer comprising a first materialover the first portion 140 of the substrate 100. Moreover, the maskingmaterial is desirably selected such that it may be selectively removedwith respect to the first semiconductor layer 130, as described below.The masking material may include a dielectric material, such as silicondioxide, silicon oxynitride, or silicon nitride.

Mask 180 may be defined after the completion of STI 160 formation.Alternatively, mask 180 may include masking material used to protectthose regions of the bilayer that are not removed during STI formation;after STI formation, the masking material may be selectively removedfrom the first portion of the substrate where the nMOSFET will beformed, thereby exposing the portion of the second semiconductor layerdisposed over the first portion of the substrate. Masking material usedduring STI formation may be, for example, a silicon nitride CMP stoplayer 182 disposed over pad oxide layer 184.

The exposed portion 310 of the second semiconductor layer 200 disposedover the first portion 140 of the substrate 100 may be removed as shownin FIGS. 7 and 8 by, e.g., RIE or by an in-situ etch prior to regrowthin the deposition tool. After the removal of the exposed secondsemiconductor layer portion 310, a first portion of the first layer 130will be exposed. A regrowth layer 330 including the first material maybe formed over the exposed first portion of the first layer 130, thusproviding a single layer including the first material for subsequent useas a channel for an nMOSFET device.

After the regrowth of the first semiconductor layer, one obtains thesame structure illustrated in FIG. 3. An nMOSFET may be formed over thefirst portion 140 of the substrate 100 and a pMOSFET may be formed overthe second portion 150 of the substrate 100, as described above withreference to FIGS. 4 and 5.

In both embodiments, a final structure may include nMOSFET and pMOSFETdevices, with each type of device having a channel of approximately thesame thickness, one type having a single-layer channel and the otherhaving a bilayer channel.

In an embodiment, regrowth layer 330 includes a semiconductor materialincluded in first and second semiconductor layers 130, 200. In thiscase, deposition of regrowth layer 330 may result in first and secondportions 140, 150 of substrate 100 both including bilayers beingdifferent combinations of materials. Referring to FIGS. 7 and 8B, inanother embodiment, exposed second semiconductor layer portion 310 isnot completely removed prior to deposition of regrowth layer 330. Inthis case, deposition of regrowth layer 330 in first portion 140 ofsubstrate 100 may result in a trilayer structure 335 including a portionof first semiconductor layer 130, a portion of second semiconductorlayer 200, and regrowth layer 330. A total thickness of this trilayerstructure may be approximately the same as the thickness of the bilayerstructure present in second portion 150 of substrate 100.

In an embodiment, after bilayer 300 or trilayer structure 335 is formedover first or second portions 140, 150 of substrate 100, an anneal isperformed to interdiffuse the bilayer or trilayer structure. The annealstep may be performed at a range of suitable temperatures and times,e.g., 800-1100° C. for 1 second-1 hour. The anneal step causes thelayers in the bilayer or trilayer to interdiffuse to form a single layerhaving a composition at least slightly different from the composition ofthe layers of the bilayer or trilayer structure. This may be desirablein order to eliminate sharp offsets in the band structure of the bilayeror trilayer structure that may affect device performance.

In an alternative embodiment, a crystalline epitaxial oxide layerdisposed over semiconductor substrate selectively induces strain infirst and second semiconductor layers disposed over the crystallineoxide layer.

Referring to FIG. 9, a crystalline epitaxial oxide layer 400 is disposedover semiconductor substrate 110. The crystalline oxide layer 400includes a material having a lattice parameter selected to exert anappropriate strain, both in terms of level and direction, on first andsecond semiconductor layers 130, 200.

For example, crystalline oxide layer 400 may include or consist of amaterial such as strontium titanate (SrTiO₃ or other compositions) orlanthanum aluminum oxide (LaAlO₃ or other compositions), having alattice parameter approximately equal to that of Si_(0.5) Ge_(0.5) thatexerts a tensile strain on Si and a compressive strain on Ge. Therefore,a first semiconductor layer including or consisting of Si disposed oncrystalline oxide layer 400 may be tensilely strained, and a secondsemiconductor layer including or consisting of Ge disposed oncrystalline oxide layer 400 may be compressively strained.

The crystalline oxide layer 400 may include or consist of amulticomponent metal oxide such as a pervoskite-type oxide having theformula ABO₃ with B including at least one acid oxide containing a metalsuch as Al, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, or Cu, and A including atleast one additional cation having a positive formal charge of fromabout 1 to about 3. Examples of such cations include cesium, strontium,barium, rubidium, yttrium, scandium, and lanthanum. Thus, examples ofappropriate multicomponent metal oxides include but are not limited to:barium strontium titanate, barium strontium zirconate, barium strontiumhafnate, lead titanate, yttrium aluminate, lanthanum aluminate, leadzirconium titanate, hafnium silicate, zirconium silicate, and rareearth-doped silicates.

Other examples of materials suitable for use as crystalline oxide layer400 include metal silicate materials, such as strontium silicon oxide(SrSiO₄), zirconium silicon oxide (ZrSiO₄), and hafnium silicon oxide(HfSiO₄), hafnium oxide (HfO₂), zirconium oxide (ZrO₂), strontiumtitanate (SrTiO₃), lanthanum oxide (La₂O₃), yttrium oxide (Y₂O₃),titanium oxide (TiO₂), barium titanate (BaTiO₃), lanthanum aluminate(LaAlO₃), lanthanum scandium oxide (LaScO₃) and aluminum oxide (Al₂O₃).

Other options crystalline oxide layer 400 include any of severaldielectric materials having lattice constants and structures similar tothat of silicon. For example, cesium oxide (CeO₂), aluminum nitride(AlN) and lanthanum aluminum oxide (LaAlO₃) all have suitable latticeconstants and crystalline structures.

Crystalline oxide layer 400 may be chosen to be deliberatelylattice-mismatched to semiconductor substrate 110 to provide a latticeconstant different therefrom for subsequent layer deposition. Thecrystalline oxide layer 400 material may be selected such that a majorcrystallographic plane of crystalline oxide layer 400 parallel to asurface of semiconductor substrate 110 differs from the crystallographicplane of that surface. This configuration may facilitate the desiredlattice match or mismatch between crystalline oxide layer 400 andsemiconductor substrate 110. For example, semiconductor substrate 110may include silicon, SiGe, or germanium with a {100} surface, andcrystalline oxide layer 400 may include an aforementioned material witha {200}, {110}, or {111} (i.e., not {100}) crystallographic planeparallel to the surface of semiconductor substrate 110. Such acombination may provide an effective in-plane lattice constant ofcrystalline oxide layer 400 suitable for lattice match or mismatch withsemiconductor substrate 110 or subsequently deposited layers. Thiscombination may also facilitate the formation of subsequently depositedlayers, e.g., first and second semiconductor layers 130, 200, having acrystallographic orientation (i.e., surface crystallographic plane)different from a surface crystallographic orientation of semiconductorsubstrate 110 and/or having an in-plane rotation of the surfacecrystallographic plane different from that of semiconductor substrate110. Such changes in crystalline orientation or rotation may result inenhanced carrier mobilities in devices subsequently fabricated on firstand second semiconductor layers 130, 200.

Crystalline oxide layer 400 may have a single composition throughout itsthickness. Alternatively, the composition of crystalline oxide layer 400may vary throughout its thickness. For example, with a ternary oxidesuch as lanthanum aluminum oxide, the lanthanum content may graduallyincrease, thus increasing the lattice constant of the layer. Suchgrading of composition in crystalline oxide layer 400 may help preventformation of defects due to lattice mismatch between crystalline oxidelayer 400 and semiconductor substrate 110. Alternatively, crystallineoxide layer 400 may include multiple crystalline oxide layers, eachhaving a different composition.

Crystalline oxide layer 400 may be formed by deposition, e.g., by CVD orALD. The crystalline oxide layer 400 has a typical thickness t₆ of about10-500 nm. Preferably, crystalline oxide 400 is thick enough to supportsubsequent deposition of first and second semiconductor layers 130, 200.Since many crystalline oxides have dielectric constants higher than thatof silicon dioxide, a thick crystalline oxide 400 may be desirable todecrease capacitance.

In another embodiment, a thin amorphous layer (not shown) is formed on atop or a bottom surface of crystalline oxide 400 to prevent defectformation at an interface between crystalline oxide layer 400 andsemiconductor substrate 110 or between the crystalline oxide layer andeither of the first and second semiconductor layers 130, 200. The thinamorphous layer may include an oxide, e.g., SiO₂, SiGeO₂, and/or GeO₂.The thin amorphous layer may be formed by a thermal treatment after theformation of crystalline oxide 400, optionally in an ambient includingoxygen.

Referring to FIG. 10, in another embodiment, a capping layer 410 may beformed on a top surface of crystalline oxide 400. The capping layer 410may protect the crystalline oxide layer 400 from various wet chemicaltreatments of the substrate prior to the formation of first and secondsemiconductor layers. If capping layer 410 includes a material that canbe removed selectively with respect to the underlying crystalline oxide400, e.g., silicon nitride or a semiconductor, crystalline oxide 400 canbe protected during subsequent masking and mask removal steps, e.g.,those steps described below.

Referring to FIGS. 11-13, after the formation of crystalline oxide 400and, optionally, capping layer 410, STI regions 160 may be defined withuse of mask 180 as described above with reference to FIG. 2. Similarly,first semiconductor layer 130 may be defined over a region of thecrystalline oxide layer disposed over the first portion 140 of thesubstrate and second semiconductor layer 200 may be defined over aregion of crystalline oxide layer disposed over the second portion 150of the substrate. First and second semiconductor layers 130, 200 may bechosen to be deliberately lattice-mismatched to the crystalline oxidelayer 400 such that the semiconductor layers are under tensile orcompressive strain. This strain may be biaxial in nature. In anembodiment, the lattice structure of crystalline oxide layer 400 is suchthat at least one of first and second semiconductor layers 130, 200 isprimarily uniaxially strained in-plane.

Preferably, if optional capping layer 410 is initially disposed over thetop surface of the crystalline oxide layer 400, then layer 410 isremoved during the formation of first and second semiconductor layers130, 200, e.g., by a wet or dry etch prior to deposition.

Subsequently, an nMOSFET may be formed, including a channel disposed ina portion of the first semiconductor layer 130 and a pMOSFET may beformed, including a channel disposed in a portion of the secondsemiconductor layer 200.

The embodiments described above include a continuous insulator layerdisposed across a wafer. In some embodiments, the insulator layer may bediscontinuous. Moreover, the insulator layer may include a firstinsulator layer including a first insulating material disposed over atleast a first portion of the substrate and a second insulator layerincluding a second insulating material disposed over at least a secondportion of the substrate. For example, different crystalline oxides maybe formed selectively in NMOS and PMOS regions. An insulator layer suchas SiO₂ may only be present below one or more device channel regions.

Referring to FIG. 14A, semiconductor substrate 110 may be used as astarting material. STI regions 160 extending into semiconductorsubstrate 110 may be defined as described above with reference to FIG.2. After STI 160 is defined, the first portion 140 of the substrate 110is exposed and the second portion 150 of the substrate is covered bymask 180, e.g., a mask defined after the completion of STI formation.Alternatively, mask 180 may include masking material used to protectthose regions of the substrate 110 that are not exposed during STIformation; after STI formation, the masking material may be selectivelyremoved from the first portion 140 of the substrate 110 where thenMOSFET will be formed, thereby exposing the first portion 140 of thesubstrate. Masking material used during STI formation may be, forexample, silicon nitride CMP stop layer 182 disposed over pad oxidelayer 184.

Referring to FIG. 14B, a first insulator layer 500 including acrystalline oxide material (and also referred to herein as “a firstcrystalline oxide layer”) may be defined over the first portion 140 ofsubstrate 110. The first insulator layer 500 may be formed bydeposition, e.g., by CVD or ALD, or a similar technique. Typically, thecrystalline oxide layer is not formed selectively; rather, it is formedover the first portion 140 of the substrate 110 as well as over the mask180 disposed over the second portion 150 of the substrate 110.Therefore, it may be preferable to mask off a region of the firstinsulator layer 500 disposed over the first portion 140 of the substrate110, prior to removal of the remainder of the crystalline oxide materialand mask disposed over the second portion 150 of the substrate 110.Alternatively, the first insulator layer 500 and a capping nitride layer(not shown) may be deposited over substantially the entire substrate110. Then a CMP step may be performed to remove the portions of thecapping nitride layer and first insulator layer 500 disposed over thesecond portion 150 of the substrate 110, stopping at a surface of themask 180 disposed over the second region 150. Any residual nitride fromthe capping layer remaining over both the first and second portions 140,150 of the substrate 110 may then be removed. This process also resultsin the formation of first insulator layer 500 over the first portion 140of the substrate 110.

Referring to FIGS. 14B and 14C, after the formation of the firstinsulator layer 500, the mask 180 is removed, thereby exposing a topsurface of the second portion 150 of the substrate. The mask 180 may beremoved by, e.g., a wet etch. During the removal of the mask 180, asmall portion of the STI 160 may also be removed, but not an amountsufficient to impact device performance. A second mask (not shown) isselectively formed over the first insulator layer 500, exposing thesecond portion 150 of the substrate. The second mask may include siliconnitride formed by, e.g., deposition, photolithography, and a wet or adry etch. A second insulator layer 510, also referred to herein as“second crystalline oxide layer,” may formed over the second portion ofthe substrate 110 by a deposition technique such as CVD or ALD. Afterthe formation of the second insulator layer 510, the second mask may beremoved by, e.g., a wet etch. The first and second insulator layers 500,510 may include the same materials and have the same thicknesses as thecrystalline oxide layer 400 described above with reference to FIG. 9.

Referring to FIG. 15, a channel layer 520 may be formed over the firstand second insulator layers 500, 510, as well as over STI region 160. Aportion of the channel layer 520 disposed over the STI region 160 may besubsequently removed by, e.g., CMP. In an alternative embodiment, afirst portion of the channel layer 520 is formed over the firstinsulator layer 500 after the formation of the first insulator layer andbefore the mask 180 is removed. Similarly, a second portion of thechannel layer 520 is formed over the second insulator layer 510 afterthe formation of the second insulator layer and before the second maskis removed. The channel layer 520 may include a semiconductor materialsuitable for device channel formation, such as a group IV material,e.g., silicon, SiGe, germanium, or an array of carbon nanotubes; a III-Vmaterial such as gallium arsenide, indium arsenide, indium galliumarsenide, indium phosphide, gallium nitride, indium antimonide, galliumantimonide, gallium phosphide; or a II-VI material, and mixtures oralloys including one or more of the aforementioned materials.

In an embodiment, the channel layer 520 includes strained silicon. Thefirst insulator layer 500 may include a material having a latticeconstant larger than that of silicon, e.g., greater than 5.43 Å,resulting in the portion of the channel layer 520 disposed over thefirst insulator layer 500 to be tensilely strained, and thereby suitablefor use as the channel material of an nMOSFET. The second insulatorlayer 510 may include a material having a lattice constant smaller thanthat of silicon, e.g., less than 5.43 Å, resulting in the portion of thechannel layer 520 disposed over the second insulator layer 510 to becompressively strained, and thereby suitable for use as the channelmaterial of a pMOSFET.

In an embodiment, a first portion of the channel layer 520 disposed overthe first substrate portion 140 differs from a second portion of thechannel layer 520 disposed over the second substrate portion 150.Different combinations of channel and crystalline oxide materials mayresult in improved device performance in different regions of thesubstrate.

In an embodiment, the use of different crystalline oxide materials infirst and second substrate portion 140, 150 facilitates the depositionof channel layers thereover that have crystalline orientations orin-plane rotations different from each other, as discussed previouslywith reference to FIG. 15. The crystalline orientation and/or rotationfor channel layer 520 may be different in first and second substrateportions 140, 150. Likewise, if different channel materials are used ineach substrate portion 140, 150, the different channel materials mayhave different orientations and/or in-plane orientations. In anembodiment, the nMOSFET channel layer in first substrate portion 140 hasa surface crystalline orientation defined by any of the {100} family ofcrystallographic planes, and the pMOSFET channel layer in secondsubstrate portion 150 has a surface crystalline orientation defined byany of the {110} family of crystallographic planes. In anotherembodiment, the in-plane rotation of the nMOSFET channel material insubstrate portion 140 is such that the nMOSFET channel is parallel toany of the <110> family of crystallographic directions, and the in-planerotation of the pMOSFET channel material in substrate portion 150 issuch that the pMOSFET channel is parallel to any of the <100> family ofcrystallographic directions.

This method of providing devices including channel materials ofcrystalline orientations and/or rotations different from each other maybe superior to other methods in which regions of different orientationsare provided prior to device fabrication. This method providesself-aligned channel materials of different crystalline orientationsand/or rotations, i.e., only in desired regions bound by deviceisolation structures. Additionally, this method enables the fabricationof device channel layers of virtually any crystalline orientation orrotation, the choice of which is not bound by and does not necessarilyrelate to a crystalline orientation or rotation of an underlyingsubstrate or of a handle wafer from which the layers may have beenbonded. This method may also be used to provide channel layers ofarbitrary crystalline orientation and/or rotation disposed overinsulator layers.

Subsequently, an nMOSFET may be formed, including a channel disposed ina portion of the channel layer 520 disposed over the first insulatorlayer 500, and a pMOSFET may be formed, including a channel disposed ina portion of the channel layer 520 disposed over the second insulatorlayer 510.

The bilayer-on-insulator constructions described above and illustratedin, e.g., FIG. 6, may give favorable carrier transport behavior forFinFET-type devices, e.g., omega FETs, tri-gate FETs, etc. FinFETstypically have gates that wrap around a channel on at least two sides ofa vertically oriented channel, allowing greater control of channelcharge than in a single gate device. This configuration also has thepotential to translate to higher drive current and lower stand-byleakage current. Devices related to the FinFET, such as the wrap-aroundgate FET (gate on both sides of as well as above the channel), alloweven more channel charge control and hence even more potential forimproved drive current and leakage current performance.

Referring to FIG. 16, in an embodiment, a FinFET may be defined asfollows. A bilayer 600 is formed by deposition of two semiconductorlayers over insulator layer 120, as described above with reference toFIGS. 1-3 and 6-8. The bilayer includes first semiconductor layer 610disposed over the insulator layer 120 and second semiconductor layer 620disposed over the first semiconductor layer 610. Both the first andsecond semiconductor layers 610, 620 may be biaxially strained. Thefirst semiconductor layer 610 may be, e.g., biaxially tensilelystrained, i.e., tensilely strained in a plane parallel to a top surfaceof the first semiconductor layer 610 and compressively strained in aplane perpendicular to the first semiconductor layer top surface. Thesecond semiconductor layer 620 may be, e.g., biaxially compressivelystrained, i.e., compressively strained in a plane parallel to a topsurface of the second semiconductor layer 620 and tensilely strained ina plane perpendicular to the second semiconductor layer top surface. Inan alternative embodiment, either of the first semiconductor and secondsemiconductor layers 610, 620 is uniaxially strained.

Referring to FIGS. 17A and 17B as well as to FIG. 16, the firstsemiconductor layer 610 may be thicker than the second semiconductorlayer 620 such that the sidewall of a fin 630 defined from the bilayer600 is primarily formed from first semiconductor layer 610. For example,the first semiconductor layer 610 may have a thickness t₁ of 40-400 Åand the second semiconductor layer 620 may have a thickness t₂ of 10-100Å. Thus, the bilayer 600 may have a total thickness t₅ of, e.g., 50-500Å.

The bilayer 600 may be patterned to define a plurality of fins 630. Inparticular, fins 630 may be defined by the formation of aphotolithographic mask (not shown) over the bilayer 600, followed byanisotropic RIE of the bilayer 600. Fins 630 may have a width w₁ of,e.g., 50-300 Å, and a height hi approximately equal to a thickness ofthe bilayer, e.g., 50-500 Å. The photomask/RIE steps also define sourcemesa region 632 and drain mesa region 634. Fins 630, source mesa region632, and drain mesa region 634 include portions of the bilayer 600 notremoved by RIE. The photolithographic mask is removed after the RIE ofthe bilayer 600.

Referring to FIG. 18, in another embodiment, fins may be formed by analternative fabrication method. A single strained semiconductor layer isdisposed over the insulator layer 120 and substrate 110. For example,the starting material may include a strained-semiconductor-on-insulator(SSOI) wafer, with first semiconductor layer 610 disposed over theinsulator layer 120. The first semiconductor layer 610 may be bonded tothe insulator layer 120. Alternatively, the insulator layer 120 mayinclude a crystalline oxide, and the first semiconductor layer 610 maybe deposited over the insulator layer. The first semiconductor layer 610may be substantially unstrained, or tensilely or compressively strained.

Referring to FIG. 19, the first semiconductor layer 610 is patterned todefine a plurality of fins 630. The fins 630 may be defined by theformation of a photolithographic mask (not shown) over the firstsemiconductor layer 610, followed by anisotropic RIE of the firstsemiconductor layer 610. The fins 630 may have a width w₁ of, e.g.,50-300 Å, and an initial height approximately equal to a thickness ofthe first semiconductor layer, e.g., 50-500 Å.

Referring to FIG. 20, a plurality of sidewall spacers 640 may be formedproximate sidewalls of the fins 630 as follows. A thin conformalinsulator layer is deposited over the fins 630 and exposed portions ofthe insulator layer 120 between the fins. The conformal insulator layermay be, for example, silicon dioxide or silicon nitride, formed by,e.g., CVD, and may have a thickness of, e.g., 100-1000 Å. The sidewallspacers 640 is defined by the removal of portions of the conformalinsulator layer by, e.g., an anisotropic dry etch, such that theremaining portions of the conformal insulator layer (which definespacers proximate the fin sidewalls) remain.

Referring also to FIG. 21, after the formation of the sidewall spacers640, a top portion of the fins 630 includes exposed portions of a topsurface of the first semiconductor layer 610 from which the fins 630 areformed. Second semiconductor layer 620 is selectively deposited on theexposed portions of the first semiconductor layer. The selectivedeposition may be performed by CVD, and the semiconductor precursor gas(or gases) may be accompanied by a Cl-containing species, e.g., Cl₂ orHCl gas. Alternatively, the semiconductor precursor gas may be achlorinated species, e.g., dichlorosilane (SiH₂Cl₂), trichlorosilane(SiHCl₃), silicon tetrachloride (SiCl₄), or germanium tetrachloride(GeCl₄). The second semiconductor layer 620 may have a thickness t₂ of,e.g., 10-200 Å. The spacers are removed, e.g., by a wet etch. In anembodiment, the top portion of the fins 630, i.e., the top portion ofexposed first semiconductor layer 610, are removed by an in-situ etchprior to deposition of the second semiconductor layer 620. Such an etchmay preserve the aspect ratio of subsequently formed bilayer fins 630.

Referring to FIGS. 21 and 16, the resulting fins 630 include secondsemiconductor layer 620 disposed over first semiconductor layer 610,like the fins formed from bilayer 600. In both embodiments, the topsurface of the fin may include a material different from the materialdisposed along a major portion of the sidewalls of the fin. In bothembodiments, both the sidewalls of the fins and the top surfaces mayexhibit a same type of strain, i.e., compressive or tensile.

In summary, this bilayer fin formation may be accomplished by formingfins from an existing bilayer material. Alternatively, the bilayer finsmay be initially defined by a single material that is then epitaxiallycapped with a second material. In both embodiments, the firstsemiconductor layer is preferably thicker than the second semiconductorlayer.

Carrier transport in FinFET device constructions may occur along threedifferent planes of the device: over a top surface of a fin and alongfirst and second sides of the fin.

If a FinFET includes a single strained semiconductor layer disposed overan insulator layer, atoms biaxially strained along one plane will havean opposite type of strain in a perpendicular plane (e.g., Si that istensilely strained in a horizontal direction will be compressivelystrained in the vertical direction due to Poisson deformation of thelattice). Hence, conduction along a sidewall of a fin covered bystrained Si will be through a compressively strained layer, andconduction along a top of the fin will be through a tensilely strainedlayer.

In some embodiments, it may be preferable to have a constructionexhibiting primarily the same strain on all three sides of the fin,i.e., both horizontally and vertically, in order to maximize themobility of carriers conducting parallel to all three sides of the fin.Therefore, a tensilely strained film may be formed over the insulatorlayer and topped with a compressively strained film. Here, most of thesidewall conduction will be through the compressively strainedsidewalls, and conduction along the topside of the fin will be throughthe other compressively strained material disposed over the tensilelystrained film.

Referring to FIG. 22, in another embodiment, the fins are at leastpartially defined in crystalline oxide layer 400. The crystalline oxidelayer may have a thickness t₇ of, e.g., 50-1000 Å. First semiconductorlayer 610, having a thickness t₁ of, e.g., 10-200 Å, is disposed overthe insulator layer including crystalline oxide. A photolithographicmask (not shown) may be defined over the first semiconductor layer 610.The photolithographic mask is, for example, photoresist. A hard mask700, such as a silicon nitride hard mask, is defined over the firstsemiconductor layer 610. This hard mask 700 may enable subsequentformation of a semiconductor layer on fin sidewalls without also formingthe semiconductor layer on the top surfaces of the fin. The hard maskmay also act as a CMP stop (see below), and may have a thickness t₈ of,e.g., 100-1000 Å.

Referring to FIG. 23, fins 630 may be defined by anisotropic RIE of thefirst semiconductor layer 610 and the crystalline oxide layer 400. Fins630 may have a width w₁ of, e.g., 50-300 Å, and a height hiapproximately equal to a sum of the thickness t₁ of the firstsemiconductor layer and at least a portion of the thickness t₇ of theinsulator layer 400, e.g., 50-500 Å.

Referring to FIG. 24, second semiconductor layer 620 may be conformallydeposited over and between the fins. The second semiconductor layer 620may be chosen to be deliberately lattice-mismatched to the crystallineoxide 400 such that the layer 620 is under tensile or compressivestrain, as appropriate. The layer 620 may contain a semiconductormaterial identical to or substantially the same as that included in thefirst semiconductor layer 610.

Referring to FIG. 25, a thick oxide fill material 710, e.g., SiO₂, maybe deposited over and between the fins 630.

Referring to FIGS. 25 and 26, a planarization step, such as a CMP step,may be performed to planarize the oxide fill material 710 and to removea top portion of the second semiconductor layer 620 disposed over thehard mask 700, thereby exposing the hard mask disposed on the tops ofthe fins 630.

Referring to FIGS. 26 and 27, after planarization, the oxide fillmaterial 710 may be removed by a wet or a dry oxide etch. Subsequently,an anisotropic dry etch may be used to remove portions of the secondsemiconductor layer 620 disposed over the hard mask 700 on the fins 630and over the crystalline oxide layer 400 between the fins 630. The hardmask 700 can then be removed by a wet or dry etch, exposing the firstsemiconductor layer 610 disposed on the tops of the fins 630.

The resulting structure has a semiconductor material disposed on threesides of a crystalline oxide fin.

As discussed previously, crystalline oxide layer 400 may be deliberatelylattice-mismatched to semiconductor substrate 110 for subsequent layerdeposition. The crystalline oxide layer 400 material may be selectedsuch that a major crystallographic planes of crystalline oxide layer 400parallel and/or perpendicular to a surface of semiconductor substrate110 is different from a crystallographic plane of the surface ofsemiconductor substrate 110. This configuration may facilitate thedesired lattice match or mismatch between crystalline oxide layer 400and semiconductor substrate 110.

For example, semiconductor substrate 110 may include or consist ofsilicon, SiGe, or germanium with a {100} surface, and crystalline oxidelayer 400 may include an aforementioned material with a crystallographicplane other than {100}, e.g., {200}, {110}, or {111}, parallel to thesurface of semiconductor substrate 110. Such a combination may providean effective lattice constant of crystalline oxide layer 400 suitablefor lattice match or mismatch with semiconductor substrate 110 orsubsequently deposited layers. This combination may also facilitate theformation of subsequently deposited layers, e.g., first and secondsemiconductor layers 610, 620, having a crystallographic orientation(i.e., surface crystallographic plane) different from that ofsemiconductor substrate 110. Such changes in crystalline orientation mayresult in enhanced carrier mobilities in devices subsequently fabricatedover fins 630.

This degree of freedom in selecting crystallographic orientation mayenable the formation of FinFETs having channel layers of arbitrarycrystalline orientation, e.g., having some FinFET channels of differentcrystalline orientation with respect to others, without necessitatingcomplicated layout issues, device rotations, or wafer bonding schemes.For example, in an embodiment, a first FinFET including a crystallineoxide and a channel layer having a substantially {100} crystallineorientation may be fabricated adjacent to a second FinFET including acrystalline oxide and a channel layer having a substantially {110}crystalline orientation. Furthermore, the first and second FinFETs maybe fabricated such the devices (e.g., the fins) are oriented in parallelto each other. Forming such a configuration may be facilitated by theuse of different crystalline oxides for each of the first and secondFinFETs. In this embodiment, the first FinFET may be an n-channel deviceand the second FinFET may be a p-channel device.

After the formation of the fins by any of the methods described above,the completion of the FinFET fabrication may continue as follows.

Referring to FIG. 28 as well as to FIGS. 17A and 17B, a gate insulatorlayer 715 is formed over the fins 630 and exposed underlying insulatorlayer 120 or crystalline oxide layer. Gate insulator layer 715 isconformally formed over fins 630, as well as over source and drain mesaregions 632, 634. Gate insulator layer 715 may include, e.g., SiO₂,SiO_(x)N_(y), silicon nitride (Si₃N₄ or other compositions), bariumoxide (BaO), strontium oxide (SrO), calcium oxide (CaO), tantalum oxide(Ta₂O₅), titanium oxide (TiO₂), zirconium oxide (ZrO₂), hafnium oxide(HfO₂), aluminum oxide (Al₂O₃), lanthanum oxide (La₂O₃), yttrium oxide(Y₂O₃), yttrium aluminate, lathanum aluminate, lanthanum silicate,yttrium silicate, hafnium silicate, zirconium silicate, and doped orundoped alloys, mixtures or multilayers, thereof and have a thickness t₉of, e.g., 10-100 Å. In some embodiments, gate insulator layer 715 isgrown, and is therefore formed only over exposed semiconductor surfaces,i.e., over top surfaces of fins 630 and source and drain mesa regions632, 634. In other embodiments, gate insulator layer 715 is deposited,and is therefore formed over an entire top surface of the fins andexposed portions of the underlying insulator layer 120 or crystallineoxide.

Referring to FIGS. 29A and 29B, a gate electrode material 720 isconformally formed over gate insulator layer 715, including over fins630. Gate electrode material 720 may include a suitably conductivematerial such as, for example, doped polysilicon, doped polycrystallineSiGe, Al, Ag, Bi, Cd, Fe, Ga, Hf, In, Mn, Nb, Y, Zr, Ni, Pt, Be, Ir, Te,Re, Rh, W, Mo, Co, Fe, Pd, Au, Ti, Cr, Cu, and doped or undoped alloys,mixtures or multilayers thereof, deposited by ALD or CVD, such as byUHVCVD, APCVD, LPCVD, or PECVD, and have a thickness t₁₀ selected fromthe range of, e.g., 100-2000 Å. A photolithographic mask (not shown) isformed over gate electrode material 720. Portions of gate electrodematerial 720 are selectively removed by, e.g., RIE to define a gate 730crossing over fins 630, and terminating in a gate contact area 740.Portions of gate insulator layer 715 are exposed (or even removed) bythe RIE of gate electrode material 720.

Referring to FIGS. 30A and 30B, a plurality of dopants are introducedinto source and drain mesa regions 632, 634 to define a source 750 and adrain 760. To form an n-type FinFET, dopants such as arsenic, antimony,or phosphorus may be implanted into mesa regions 632,634. Suitableimplantation parameters may be, for example, arsenic with a dose of2×10¹⁵ atoms/cm² implanted at an energy of 10-50 kilo-electron volts(keV). To form a p-type FinFET, dopants such as boron or indium may beimplanted into mesa regions 632, 634. Suitable implantation parametersare, for example, boron, with a dose of 2×10¹⁵ atoms/cm² at an energy of3-15 keV. For the formation of a CMOS device, NMOS regions may beprotected by a mask during the implantation of p-type dopants into PMOSregions. Similarly, PMOS regions may be protected by a mask during theimplantation of n-type dopants into NMOS regions. A suitable mask forboth types of implantation may be, e.g., photoresist.

During the introduction of dopants into source and drain mesa regions632, 634, a plurality of gate dopants 775 may also be introduced intogate 730 and gate contact area 740. Gate dopants 770 serve to increase aconductivity of gate electrode material 720. Gate dopants 770 may be,for example, implanted arsenic, antimony, or phosphorous ions for ann-type FinFET.

Dopants for both n-type and p-type FinFETs may be implanted at an angleof 20-50°, with zero degrees being normal to the substrate 110.Implanting at an angle may be desired in order to implant ions into aside of exposed fins 630 and also into a side of the vertical surfacesof gate electrode material 720.

Referring to FIGS. 31A and 31B, a blanket layer of spacer insulatormaterial is formed over the substrate 110, including over gate 730, gatecontact area 740, source 750, and drain 760. Spacer insulator materialmay be, for example, SiO₂ or Si₃N₄ deposited by CVD and have a thicknessof, for example, 100-1000 Å. Subsequently, portions of spacer insulatormaterial are removed by an anisotropic RIE to define a plurality ofsidewall spacers 775 proximate vertical surfaces, such as fins 630, gate730, and gate contact area 740. Horizontal surfaces, such as topsurfaces of fins 630, are substantially free of the spacer insulatormaterial.

After the RIE definition of sidewall spacers 775, the portions of gateinsulator layer 715 exposed by the RIE of gate electrode material 720may be removed from top surfaces of source 750, and drain 760 by, e.g.,a dip in hydrofluoric acid (HF), such as for 5-30 seconds in a solutioncontaining, e.g., 0.5-5% HF. Alternately, this removal may be via RIE,with an etchant species such as, e.g., CHF₃.

Referring to FIGS. 32A and 32B, a salicide is selectively formed overthe substrate 110 to provide low-resistance contacts to the source anddrain regions and the gate electrode as follows. A conductive layer isformed over the substrate 110. For example, a metal such as titanium,platinum, zirconium, cobalt, nickel, or alloys, mixtures, or multilayersthereof is deposited by, e.g., CVD or sputtering, with the conductivelayer having a thickness of, e.g., 50-200 Å. An anneal is performed toreact the conductive layer with the underlying semiconductor, e.g.,exposed portions of gate 730 and gate contact area 740, to form salicide780 including, e.g., cobalt silicide or nickel silicide. Annealparameters may be, for example, 400-800° C. for 1-120 seconds. Unreactedportions of the conductive layer disposed directly over insulatormaterial, such as exposed portions of insulator layer 120 and sidewallspacers 775, are removed by a chemical strip. A suitable chemical stripmay be a solution including H₂SO₄:H₂O₂ at a ratio of 3:1. A secondanneal may be performed to further lower resistivity of salicide 780.The second anneal parameters may be, for example, 600-900° C. for 1-120seconds. A FinFET 790 includes fins 630, gate insulator 715, source 750,drain 760, and gate 730, and an exemplary FinFET 790 having three fins630 is illustrated in FIG. 32B. The three fins 630 share a common source750 and a common drain 760. A single transistor may have multiple finsto increase current drive in comparison to a transistor with a singlefin. The semiconductor material disposed in each fin 630 defines adevice channel.

In an alternative embodiment, gate dielectric material may be removedfrom the top surfaces of the source and drain mesa regions immediatelyafter the RIE of the gate electrode. In some embodiments, raised sourceand drain regions may be formed, as described above with reference toFIGS. 4 and 5.

Referring to FIG. 14C as well as to FIGS. 33A-33C, a structure includingfirst and second insulator layers 500, 510 disposed over first andsecond portions 140, 150 of semiconductor substrate 110, respectively,may be used to fabricate a first FinFET 790 a and a second FinFET 790 bthat are physically parallel to each other and have channels withdifferent crystalline orientation. Such first and second FinFETs may befabricated as follows.

First insulator layer 500 disposed over the first portion 140 ofsemiconductor substrate 110 may include a first crystalline oxide, andsecond insulator layer 510 disposed over the second portion 150 ofsemiconductor substrate 110 may include a second crystalline oxide. Thefirst and second crystallographic oxides may be identical, substantiallythe same, or substantially different. First semiconductor layer 610 acomprising a first semiconductor material is disposed over the firstinsulator layers 500, and first semiconductor layer 610 b comprising asecond semiconductor material is disposed over the second insulatorlayer 510. In an embodiment, first and second semiconductor materialsare identical or substantially the same. In an alternative embodiment,first and second semiconductor materials are different. In bothembodiments, the first semiconductor material disposed in firstsemiconductor layer 610 a has a first crystalline orientation, thesecond semiconductor material disposed in first semiconductor layer 610b has a second crystalline orientation, and the first and secondcrystalline orientations are different.

A first plurality of fins 630 a disposed over the first insulator layer500, and a second plurality of fins 630 b disposed over the secondinsulator layer 510 are defined as discussed above with reference toFIG. 23-27, with a second semiconductor layer 620 a comprising the firstsemiconductor material disposed on the vertically oriented sidewalls ofthe fins 630 a, and a second semiconductor layer 620 b comprising thesecond semiconductor material disposed on the vertically orientedsidewalls of fins 630 b. At least one fin from the first plurality offins 630 a may be parallel to at least one fin from the second pluralityof fins 630 b. The term “vertically oriented” does not denote aparticular absolute orientation; rather, it is used herein to mean anorientation that is substantially perpendicular to a top surface of thesubstrate over which the fin is formed.

In the embodiment in which the first and second semiconductor materialsare different, second portion 150 of substrate 110 may be the portion ofthe substrate including second insulator layer 510, and may be protectedby a masking material during fabrication of the first FinFET 790 a.Likewise, after the first FinFET 790 a is fabricated, it may beprotected by a masking material during fabrication of the second FinFET790 b. Alternatively, the same channel material, i.e., semiconductormaterial, may be deposited over both first and second insulator layers500, 510 as described above with respect to FIG. 15, and the first andsecond FinFETs 790 a, 790 b may be fabricated in turn as described abovewith reference to FIGS. 22-27.

The first FinFET 790 a includes fins 630 a, gate insulator 715, source750, drain 760, and gate 730. The second FinFET 790 b includes fins 630b, gate insulator 715, source 750, drain 760, and gate 730. Both FinFETs790 a, 790 b may include gate contact areas 740, sidewall spacers 775,and salicide regions 780.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The foregoingembodiments are therefore to be considered in all respects illustrativerather than limiting on the invention described herein.

1. A method for forming a structure, the method comprising: providing asubstrate having an insulator layer disposed thereon, and a bilayerdisposed in contact with the insulator layer, the bilayer including asecond semiconductor layer disposed over a first semiconductor layer;and thereafter forming a fin field-effect transistor on the substrateby: patterning the bilayer to define a source region, a drain region,and at least one fin disposed between the source and the drain regions,forming a gate dielectric layer at least a portion of which is disposedover the fin, and forming a gate over the gate dielectric layer portiondisposed over the fin, wherein a thickness of the first semiconductorlayer is greater than a thickness of the second semiconductor layer suchthat a sidewall of the fin is primarily defined by the firstsemiconductor layer.
 2. The method of claim 1, wherein the bilayercomprises at least one of a group II, a group III, a group IV, a groupV, or a group VI element.
 3. The method of claim 1, wherein the bilayercomprises a strained semiconductor layer.
 4. The method of claim 3,wherein the strained semiconductor layer is tensilely strained.
 5. Themethod of claim 3, wherein the strained semiconductor layer iscompressively strained.
 6. The method of claim 1, wherein the insulatorlayer has a thickness between 10 and 50 nm.
 7. The method of claim 1,wherein a sum of the thickness of the first semiconductor layer and thethickness of the second semiconductor layer is 0.25 to 0.7 times a gatelength of the fin field-effect transistor.
 8. The method of claim 1,wherein a sum of the thickness of the first semiconductor layer and thethickness of the second semiconductor layer is less than 50 nm.
 9. Themethod of claim 1, wherein the thickness of the first semiconductorlayer is between 5 and 10 times greater than the thickness of the secondsemiconductor layer.
 10. The method of claim 1, wherein the thickness ofthe second semiconductor layer is between 1 and 10 nm.